It can be difficult to prevent newly manufactured glass and other substrates from accumulating contaminants from the manufacturing environment. Manufacturing environments commonly contain organics and other residues that can contaminate the substrates being produced. For example, various solvents, curing products, and sealants used in manufacturing glass and glass products produce residues that can accumulate on the glass being produced. The atmosphere in the manufacturing facility may also contain vapors that condense on, or otherwise contaminate, the manufactured glass. For example, silicone is commonly used as a sealant in the manufacture of insulating glass units (IG units). Newly deposited silicone may outgas for significant periods of time. As a consequence, glass may accumulate silicone residue after simply being exposed to an ambient manufacturing environment. In fact, it has been discovered that this type of silicone contamination is very difficult to prevent. Unfortunately, silicone contamination can also be extremely difficult to remove.
Contamination can occur in several other ways during manufacturing processes. For example, glass sheets are commonly conveyed across rollers as they are coated. During conveyance, the bottom surface of the glass is in supportive contact with the rollers, which can leave minor impurities or traces of contact. While these imperfections tend to be very slight, they are unwanted and should be avoided if possible. Handling equipment used in producing glass products can also leave marks on the glass. For example, vacuumized suction cups are commonly used to handle glass sheets. This has been found to leave suction cup marks on the glass, at least in some instances. Stickers and other markings may also be applied during glass production. These stickers and markings tend to be easily removed. However, it can be difficult to assure they will have no permanent effect on the glass surfaces from which they are removed.
Glass sheets and other substrates are subjected to other contamination sources after leaving the manufacturing facility. For example, glass products may be exposed to a variety of storage and transport environments before reaching their final destination. Like manufacturing facilities, storage and transport environments may contain residues and vapors that can accumulate on and contaminate the products therein. For example, IG units and other products found in storage and transport environments may contain silicone sealants and other materials that can outgas for substantial periods of time. Of course, many of these environments are outside the manufacturer's control. Thus, while a manufacturer may attempt to control the environment within its own manufacturing and storage facilities, it would be very difficult to regulate each of the environments to which glass may be exposed prior to delivery to the ultimate consumer.
Contamination can also occur when glass products are installed or finished. The contamination that is perhaps most familiar to new homeowners occurs when window frames are painted and some of the paint unintentionally ends up on a window pane. While installers and painters can take steps to temporarily mask the surfaces of nearby glass (e.g., by applying “masking tape”), it can be difficult to mask the entire surface of the glass. Thus, any unmasked surface areas will still be vulnerable to unintentional spills and drips. Moreover, to the extent these tapes are applied with adhesive, it can be difficult to assure that no adhesive residue is left on the glass following removal.
Contamination sources like these can make it exceedingly difficult to manufacture, transport, install, and finish glass and other substrates that are free of surface contamination. The most obvious solution to this problem would be to simply remove the surface contamination, such as by washing or otherwise cleaning the contaminated surface. For example, various polishing and etching agents have been used to remove paint contamination from window panes. Technicians have even been known to use razorblades to scrape paint and the like off glass. Unfortunately, these aggressive treatments may actually remove some of the glass, leaving dull or scratched areas. Even with aggressive cleaning methods, certain contaminants (e.g., silicone) can be virtually impossible to remove.
Another solution would be to temporarily protect substrates during periods of potential contamination. In the past, attempts have been made to protect glass with removable papers and plastics. Typically, these papers and plastics are removed by mechanically peeling them from the substrate. Reference is made to U.S. Pat. No. 1,256,818 (Nile), U.S. Pat. No. 5,107,643 (Swensen), and U.S. Pat. Nos. 5,599,422 and 5,866,260 (both to Adams, Jr. et al.), the entire contents of each of which are incorporated herein by reference.
Unfortunately, protective papers and plastics have a number of disadvantages. For example, they are commonly applied using adhesives. These adhesives may react with glass, rendering them difficult to remove and possibly altering the surface properties of the glass. This may be particularly likely in cases where the glass is masked for long periods of time or where the masked glass is exposed to high temperatures or substantial radiation (e.g., sunlight). Components of certain papers and plastics, such as those containing silicone, may also react with glass in these ways. Non-adhesive applications, such as those relying on static cling, would seem possible. However, papers and plastics applied in this manner may be less secure than desired, perhaps even falling off during handling. Further, when protective papers and plastics are removed, they generate additional waste that must be discarded or recycled, thus creating additional labor and expense.
Attempts have also been made to temporarily protect glass by applying liquid coating compositions through a variety of wet deposition processes (e.g., painting, dipping, or spraying). While the resulting coatings vary in composition, many of them are polymeric materials that are removed by peeling or by washing with water. Reference is made to U.S. Pat. No. 5,453,459 (Roberts), U.S. Pat. Nos. 5,866,199 and 6,124,044 (both to Swidler), and International (PCT) Publication Numbers WO 00/50354 (McDonald) and WO 01/02496 (Medwick et al.). The Medwick et al. reference also discloses a sputtered carbon-containing coating that can be used to temporarily protect glass. The coating is said to be removable by combustion. For example, Medwick et al. expressly indicate that their coating would be oxidized and removed during tempering. Unfortunately, all of these approaches are less than ideal.
The limitations of these approaches become more apparent when one considers the full scope of processing that a typical window endures. Glass sheets can be formed by a number of processes, perhaps the most common of which is the float glass process. In this process, the basic elements of glass are combined and heated in a furnace to temperatures on the order of 2900° F., whereby the glass becomes molten. A ribbon of this glass is then floated atop a molten tin bath where it begins to cool and is machined to a desired width and thickness. The glass is then cut into smaller sheets.
Glass sheets can be coated with a variety of different coatings using a variety of different coating methods. Sputter deposition is a common method for applying coatings to large area substrates, such as glass for architectural applications. When glass sheets are coated by sputter deposition, the sheets are conveyed into a sputtering chamber. Typically, the glass is conveyed through a series of connected sputtering chambers (i.e., a sputtering line), each containing a controlled sputtering atmosphere. As the glass sheets are conveyed through the sputtering line, the desired coatings are sputtered onto the glass. At the outlet of the sputtering line, the glass is removed from the controlled sputtering atmosphere and is exposed to the ambient glass processing atmosphere. At this point, the coated glass may begin to accumulate contamination from the environment.
Thus, coated glass is typically vulnerable to becoming contaminated once it is removed from a controlled coating environment. As a consequence, it would be desirable to apply temporary protection to a coated substrate at the same time the substrate is coated. For example, it would be desirable to apply a temporary protective cover over sputter-coated glass before removing the glass from the sputtering line.
It would likely be difficult to apply papers, plastics, or liquid coating compositions inside a sputtering chamber. For example, the elevated substrate temperatures that occur during sputtering would tend to make application challenging. During sputtering, glass commonly reaches temperatures on the order of 100-200° C., and may reach even higher temperatures for certain processes. These temperatures would be above the softening points of many plastics and many adhesives used to apply papers or plastics. Further, conventional sputtering chambers are not configured for wet deposition processes. Thus, it would likely be impractical, if not impossible, to apply any of these protective materials in a sputtering chamber. Even if it were feasible to apply these protective materials in a sputtering chamber, these materials may not withstand the processing to which many substrates are subjected after they are coated.
Once glass is removed from a coating atmosphere (e.g., a sputtering chamber), it is typically covered with a so-called “separator”. Typical separator comprises a protective powder (e.g., adipic acid powder), which protects the glass against moisture corrosion. The powder commonly contains small beads (e.g., nylon beads), which separate the glass sheets when they are stacked against one another. These beads prevent the surfaces of adjacent sheets in a stack from coming into contact with one another, thereby minimizing abrasion and other damage.
As noted above, glass sheets are sometimes assembled into IG units. As one of the first steps in this process, the separator is typically washed from the glass sheets. This is conventionally accomplished by passing the glass sheets through industrial glass washing machines. Industrial glass washers typically apply water, which may be hot, and optional detergents to the glass. Most protective papers and plastics would not be expected to survive being run through an industrial glass washer. Moreover, deterioration of these materials could create a terrible mess inside a washing machine, perhaps clogging the machine and complicating its maintenance. Further, many protective materials that are applied in liquid form are water soluble. Thus, it would be desirable to provide a temporary protective cover that is durable to industrial washing.
Coated glass may also be subjected to various elevated temperature processes, such as heat tempering or bending. During tempering, for example, glass is commonly heated to temperatures on the order of about 600° C. (1112° F.) for substantial periods of time (e.g., hours). Unfortunately, most protective papers, plastics, and polymeric materials would be burned-off, or at least significantly deteriorated, during elevated temperature processing. Likewise, the carbon-containing protective coating described in the Medwick et al. reference is said to be burned-off during tempering. Since tempered glass may be exposed to contamination sources after tempering (e.g., during subsequent storage, transport, installation, and finishing), it would be advantageous to provide a temporary protective cover that is durable to tempering.
It would be desirable to provide temporary protective covers that can be applied to coated substrates as part of the coating process. For example, it would be advantageous to provide temporary covers that can be applied to sputter-coated glass in the controlled sputtering environment. It would be particularly desirable to provide temporary covers that are sufficiently durable to withstand the full scope of processing that glass and other substrates typically endure. For example, it would be advantageous to provide temporary covers that are durable to industrial glass washing and the like. It would be especially desirable to provide a temporary cover that is durable to elevated temperature processing (e.g., heat tempering and bending). At the same time, it would be desirable to provide a temporary cover that can be readily removed after installation or finishing, or at any stage when it is desired to expose the underlying surface.